1. Field of the Invention
The present invention relates to a semiconductor device. In particular, the present invention relates to a semiconductor device using a multilayer board.
2. Description of Related Art
In a multilayer board of a semiconductor device using a BGA (Ball Grid Array) package, a power source plane and a GND (Ground) plane are generally provided in an inner layer. The general power source plane and the GND plane are each a sheet of conductor that spreads to be an area being as large as possible in the layer, basically.
Generally, the general power source plane and the GND plane are opposed to each other in a same area. This causes a generation of needless RF (radio frequency) radiation due to the electromagnetic coupling between these two planes. In this case, since radiated to the outside of a package of the semiconductor device, there is a possibility that the RF radiation badly affects external circuits or device.
As a method for preventing the RF radiation from being leaked to the outside of the semiconductor device, a technique for wrapping the power source plane with another conductor, for example, is known.
Regarding the above description, Patent Document 1 (Japanese Patent Application Publication JP2003-218541A) discloses a description according to an EMI reducing structure board. The EMI reducing structure board includes a sheet conductor for power source, a dielectric substance, two sheets of sheet conductors for ground, and a sheet conductor for connection. Here, the dielectric substance entirely wraps the surface of the sheet conductor for power source. Moreover, two sheets of the sheet conductors for ground and the sheet conductor for connection configure one conductor of closed area, and the closed area conductor further wraps the sheet conductor for power source wrapped by the dielectric substance. That is, two sheets of the sheet conductor for ground sandwich the sheet conductor for power source wrapped by the dielectric substance from the surface and the reverse surface. The sheet conductor for connection is connected to two sheets of the sheet conductor for ground, and entirely surrounds side surfaces of the sheet conductor for power source wrapped by the dielectric substance.
In addition, Patent Document 2 (Japanese Patent Application Publication JP2004-363347A) discloses a description regarding a multilayer printed circuit board. The multilayer printed circuit board includes signal layers, two sheets of power source layers, insulation layers, two sheets of ground layers, and a shield. Here, two sheets of the power source layers are arranged to be parallel with and to be separated from each other. The signal layers are arranged between two sheets of the power source layers to be parallel with and to be separated from each other. The insulator of the insulation layers entirely wraps the surfaces of the power source layers and signal layers. Two sheets of the ground layers and the shield are connected and configure one conductor of closed area, and the closed area conductor further wraps the power source layers and signal layers each wrapped by the insulator. That is, two sheets of the ground layers sandwich the insulator wrapping these power source layers and signal layers from the surface and reverse surface thereof. The shield is connected to two sheets of the ground layers, and entirely surrounds side surfaces of the power source layers and signal layers wrapped by the insulator.